Pile-driving mandrel



United States Patent PILE-DRIVING MANDREL Walter H. Cobi, Port Chester, N .Y. Application August 17, 1954, Serial No. 450,405 7 Claims. (CI. 61-79) The invention relates to expansible pile driving mandrels and particularly to expansible mandrels or cores capable of insertion into the empty shell or mold for a concrete or cast-in-place pile and of driving the shell into the ground under hammer blows.

The invention particularly relates to the arrangement of the bottom end of a mandrel of this general type.

A driving mandrel or core, such as referred to, is mainly composed of a driving head portion, a driving boot portion and the core portion extending therebetween for transmitting the hammer blows imparted to the head portion throughout the length. of the outer shell to the boot portion contacting the earth. In some constructions the driving boot portion includes a heavy footplate, which is located inside an outer shell-like boot. The footplate is attached more or less-loosely .to the lower end of the mandrel and extends transversely below the lower end thereof, whereas the shell-like boot surrounds the plate on bottom and sides and is attached to the lower edge of the shell. Thus the blows will be received by the heavy plate from the core elements and imparted to the boot for direct action on the earth.

Whereas both foot plate and boot cooperate with the core portion of the mandrel in the driving action into the earth, only the plate is retrieved when the mandrel is extracted from the shell.

In the general construction of driving boot portion referred to, the footplate is particularly useful in that it protects the lower end of the mandrel and may readily be replaced if badly deformed during operation. -When,

this construction is used for the type of mandrel in which the core portion is made up of a plurality of parallel core elements extending to the bottom end of the shell, as in the pneumatic type of mandrel, the single footplate extends under the ends of all the core elements and thus serves the further purposeof combining the forces from the core elements and applying the resultant force to the bottom area of the outer boot. The plate thus tends to equalize possible differences in the forces from the core elements and, by virtue of its uniform contact with the bottom of the boot, distributes the resultant force evenly over that bottom, so that any tendency of the earth to force the boot sideways during a blow is counteracted.

The boot usually has a collar rising from the bottom area thereof which is attached, as by welding, to the lower edge of the shell. The boot thus further serves to protect the edge of the shell against serious deformation and I ripping. 7

However, due to the rough treatment to which pile equipment is subjected as a result of continuous heavy hammering against hard layers or rock in the ground, it has been found diflicult at times to clear the footplate out of the boot and shell when these have been deformed by being driven against suchobstacles.

These difliculties, when not too severe, have in some cases been overcome by giving the heavy footplate the 2 shape of a truncated cone with the smaller diameter on the upper side. When the plate is being lifted out it will thus have a tendency to wedge its way through deformations of the edges of the boot and shell, which remain in the ground. This partial remedy has however the serious disadvantage of leaving the upper edge of the collar on the boot unsuported by the foot plateagainst the heavy side pressure exerted by the earth during driving. This side pressure thus may force the upper edge of the collar inward far enough to prevent the footplate from passing for removal from the boot and shell.

It is an object of my present invention to provide an especially efficient arrangement of driving parts at the lower driving end of the mandrel.

It is a more particular object to provide an arrangement of such driving parts that will be highly effective in operation, will withstand heavy strains without serious deformation, and will not interfere with the extraction of the contracted mandrel from the driven shell upon completion of the driving operation under conditions such as are usually encountered.

It is a still further object to provide a boot portion which during operation is substantially fully backed up by the interior parts against deformation.

It is a specific object to' provide an improved bootportion, including driving boot and foot plate, in which the driving force will be distributed over substantiallythe total area available within the shell or mold.

In accordance with a principal feature of the invention the driving boot and the footplate are shaped and dimensioned both to present active surfaces contacting the bottom end of the core portion for reception of the force blows therefrom and to present active surfaces which will permit utilization of substantially the whole cross sectional area within the casting shell for transmission of the force blows from the core portion tothe earth, thereby imparting to the mandrel a tendency toward straightline driving.

In accordance with more specific features of the invention the driving boot is shaped to have a collar for attachment to the lower end of the molding shell, an annular shoulder extending inward from the collar to engage the outer part of the bottom end of the core portion for reception of driving force therefrom, and a central cavity serving as location for a heavy foot plate engaging the more central part of the bottom end of the core portion for reception of driving force therefrom,

In accordancewith-still other features the collar of the boot extends upward 0n the outside of the shell for protection of the lower edge of the shell against outside pressure from the earth, and the collar at the same time provides space within the boot for the lower end of the driving core elements which, when expanded during driving, act to give radial support to the collar and prevent it from buckling inward.

The features and advantages of the invention will be understood from the following description and the accompanying drawing which disclose a preferred practical embodiment thereof. It should be understood that the invention is not intended to be limited by the terms or expressions used in this description, nor by the specific details or arrangements of parts shown in the drawing. The scope of the invention in its various aspects is defined'by the attached claims.

Reference will now be made to the attached drawing which shows an arrangement in accordance with the invention which will overcome or alleviate the difliculties encountered hitherto, as referred to above.

In the drawing: Figure 1 is a simplified view of a complete driving mandrel with a casting shell;

Figure 2 is a detail view in perspective showing the Patented Apr. 26, 1960 lower end of the mandrel, certain parts being shown broken away;

Figure 3 is a perspective view of thedriving boot; and Figure 4 is a perspective view of the foot plate.

Fig. 1 shows the general arrangement of. a driving mandrel, expanded and ready for driving. It includes the driving head 10, which receives the hammer blows from a driving rig, not shown. The head may have two holes 12 through the body portion thereof through which steel cables from the rig maybe threaded for raising or lowering the whole mandrel. The mandrel further includes a driving boot portion 14 and a core portion 16, said core portion being surrounded over its entire length by the mold or shell 18, the middle portion of which is shown broken away. The core portion 16 is shown as being continuous throughout the length of the mandrel; it may however be made up of interconnected sections. It may be connected 'to the head in any desired manner, without serious reduction of the area of engagement with the head for reception of the blow force therefrom. The shell 18 is of the corrugated type having transverse corrugations in immediate succession along its entire length. 7

The details of the core portion 16 and the driving boot portion 14 are more clearly shown in Fig. 2.

The mandrel 16 is shown here, for purposes of illustration, as being of the expansible pneumatic type, although it will be understood that the invention is also applicable to mechanically expanded mandrels. Considering the cross section of said mandrel 16, it will be noted that it includes pneumatic hose means or fluid pressure containers 20 located between a plurality of angle iron segments 22, each of which is welded to the inside surfaces of a curved surface plate 24. The plates 24 form the surface or body of the core portion 16 of the mandrel. When the hose means is inflated it presses the segments 22 outward so that the surface plates 24 will come into tight contact throughout their length with the shell 18, in order that the driving force may be partly applied to the shell to overcome resistance against the sides of the driven hole. When the hose means is deflated a. plurality of springs (not shown) between opposit'esegments 22 will withdraw the surface plates 24 from contact with the shell so that the core body may be withdrawn therefrom. Pneumatically operated core segments, constructed and operating as above described, and connected at one end of the mandrel core to a driving head and at the opposite end to a foot plate, are shown in my pending application Serial No. 358,357, filed May 29, 1953; now Patent No. 2,881,592 and are now well known in the art through extensive use. b

Each of the surface plates 24 may have a series of bars 26 attached to its outer surface, and disposed helically or circularly thereon. The bars are distributed along the whole length of the plate with a suitable spacing and are in alignment with the corrugations in the shell 18. When the core 16 is expanded the bars 26 fall into corresponding corrugations and thus provide added friction or support for driving the shell through the hole made by the boot portion 14.

The boot portion 14 of the mandrel includes the shell like boot 30 and the foot plate 32.

The boot comprises a cylindrical collar 34 which fits on the outside surface of .the casting shell 18 and may be welded thereto. In the instance of the shell having spirally disposed corrugations the upper edge 36 of the collar may be tongued, as shown in Fig. 3, to match the corrugations. The tongues may thus be bent into corresponding corrugations and welded thereto.

The boot further has an annular shoulder 38 along the bottom edge of the collar which in turn fringes a depression 40 with sloping sides and 'a bottom which, as shown in the drawing, is substantially flat. The boot is preferably of malleable iron, and punched out of sheet iron in order to withstand sudden impact with rock withsnaaaa'ai 4 out cracking. For a mandrel about 12" in diameter the wall thickness may be about The foot plate 32 is shaped as a truncated cone with sides and bottom that will fit into the depression 40 in the boot. The height is such that the top surface 42 will be practically flush with the inside shoulder surface 38 of the boot. The plate is preferably of billet steel or other suitable steel, and has a central shouldered hole 44 for a treated end-washer and nut 46 of a shouldered post 48 thus secured in the hole. The post 48 carries at its upper end a crossbar 50 which extends in both directions through holes 52 (only one being shown) in diametrically opposed segments 22 of the core portions 16, as in my aforementioned application, so that the plate will follow the core when the mandrel is inserted into or removed from the shell 18. A hole 54 in the post for passing the crossbar 50 is slightly oblong in order to relieve the crossbar 50 of strain from the blow forces. The bar passes freely through the holes in the segments 22 as these move in and out when the mandrel is contracted and expanded.

When the parts have been assembled the plate 32 sets snugly in the cavity 40 of the boot 30 with its upper larger surface 42 flush with the upper surface of the shoulder 38. The surfaces 42 and 38 thus are in working contact with the flush bottom surfaces of the seg' ments 22 and curved plates 24, so that the force blows from the core elements will be practically completely met by the counter pressure from the earth through the boot and plate.

It should be noted that the upright collar 34 is backed against heavy peripheral forces from the ground by the lower end portions of the corrugated shell 18 and the curved plates-24 of the expanded mandrel, whereby any tendency of the collar to buckle inward will be strongly opposed. Thus the entire boot is strongly backed in all areas against external forces.

It should be further noted that by the above-described construction embodying the invention the provision of an annular shoulder of the boot permits of a reduced greatest diameter of the foot plate 32, so that the foot plate may be retracted in spite of appreciable deformation of the boot and shell. Thus the greatest diameter of the plate 32 may be at least two inches smaller than the inside diameter of the shell 18 and may be less than the diameter of the contracted core portion 16. The

foot plate nevertheless extends under the ends of all the core elements to combine the forces therefrom, and, by its sturdiness, equalize possible differences in these forces. 7

The terms and expressions which I have employed are used as terms of description and not of limitation, and I have no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described or portions thereof, but recognize that various modifications are possible within the scope of the invention claimed.

Iclaim':

1. A driving boot for connection to the lower end of a cylindrically shaped pile casting shell having spiral corrugations in its cylindrical wall, said boot comprising an upstanding cylindrical wall portion in the form of a collar adapted to extend around and engage the outer surface of the lower portion of a spirally corrugated shell, an annular shoulder extending inwardly from the lower end of said collar portion having a surface in a plane at right angles to the axis of said collar, and a central depressed portion of truncated cone shape extending downwardly from the inner periphery of said annular shoulder with the smaller surface of said truncated cone atthe bottom of said boot, said smaller surface lying in a plane substantially parallel to the plane of said annular shoulder, the upper end of the cylindrical wall portion of said collar having upwardly extending tongues spaced circumferentially around said wall portion.

2. Pile driving equipment which comprises an elongate pile shell; a driving mandrel within said shell having a core portion comprising expansible and contractible segments having vertical curved wall portions at their peripheries and a foot plate secured to the bottom end of said core portion; and a driving boot secured to the lower end of said shell; the vertical curved walls of said segments frictionally engaging the inner surface of said shell whensaid segments are in expanded condition, said boot comprising an upstanding collar portion in the form of a vertical wall surrounding and engagingthe peripheral surface of the lower end of said shell, an annular shoulder wall portion extending inwardly'from the lower end of said collar portion having an annular substantially horizontal upper'surface under the lower ends of the curved walls of the core when said segments are expanded and providing a central opening in the upper end of said boot, walls forming a central truncated cone shaped cavity in said boot open at its upper end, said truncated cone shaped cavity extending downwardly from said annular shoulder wall with the smaller surface of said truncated cone at 'the bottom of said boot, said smaller surface lying in a plane substantially normal to the axis of said shell, said foot plate having a truncated cone shape and fitting snugly but removably in said cenprising expansible and contractible segments within said shell, the segments of said core having curved wall portions engaging the inner surface of said shell when they:

segments at the lower end of said core, a driving boot tral cavity and having a diameter at its upper surface no greater than the diameter ofsaid core portion when said segments are in contracted position, so that said core portion together with said foot plate maybe removed from said shell when saidseg'ments are moved to contracted position after said shell is driven into the ground.

3. Pile driving equipment which comprises an elongate pile shell; a driving mandrel within said shell having having an upstanding collar surrounding and secured to the lower end of said shell and having an annular shoulder extending inwardly from the lower end of said collar and a tapered wall of truncated cone shape extending downwardly from said shoulder, the upper end of said truncatedcone being openan'd said tapered wall extending downwardly fromthe inner periphery of said annular shoulder, the lower end of said truncated cone being closed by a flat circular wall having a diameter smaller than the diameter of the upper open end of said truncated cone, said flat circular wall lying in a plane substantially normal to the axis of said shell, said truncated cone portion forming a centrally depressed central cavity of truncated cone shape closed at its lower end, said foot plate having a truncated cone shape come plementary to said central cavity of fthe boot, the lower edges of said curved wall portions of said core segments engaging said annular shoulder and said foot plate engaging the inner surfaces of said central cavity of the boot when said mandrel is in pile driving position and expanded in said shell, the diameter of the upper surface of said foot plate being no greater than the diameatcore portion comprising expansible and contractible segments having vertical curved wall portions and a foot plate secured to the bottom end of said core portion; and a driving boot secured to the lower end of :said shell; said boot comprising an upstanding collar portion in the form of a cylindrical wall surrounding and engaging the peripheral surface of the lower end of said shell, an annular shoulder wall portion extending inwardly from the lower end of said collar portion having an annular substantially horizontal upper surface, a truncated cone shaped wall portion extending downwardly from the inner periphery of said annular shoulder and a bottom wall portion closing the 'lower and smaller end of said truncated cone portion, said bottom wall lying in a plane substantially normal to'the axis of said shell, said truncated cone and bottom wall portions defining a central truncated cone. shaped cavity having an open upper end, said foot plate being in the shape ter of said core when its segments are in contracted condition sothat said core together with'said foot plate may be removed from saidshell after said shell has been driven into the ground. a

5. Pile driving equipment constructed according to claim 4 in which the foot plate has a central shouldered vertically disposed hole through which extends a post having a nut screwed thereon in said hole below the shoulder of said hole for removably securing said plate to the segments of said core.

6. Pile driving equipment constructed according to claim4 in which the upper surface of said foot plate lies flush with the surface of said annular shoulder of the driving boot when said mandrel is in 'pile driving position in said shell.

7. Pile driving equipment constructed according to claim 4 in which the casting shell is spirally corrugated of a truncated cone and snugly but removably fitting,

in said central cavity with its tapered sidewall engaging the tapered side wall of said boot and its bottom end engaging the bottom wall of said boot, and the vertical curved walls of said segments engaging the inner,

surface of said shell and the ,lower edges of said curved walls of said segments engaging said annular horizontal surface of said driving boot when said core segments are expanded and the mandrel is in pile' driving position so that forces of driving blowsimparted to said core are transmitted through said curved 'wallsto said annular shoulder and throughsaid foot'plate to the tapered side wall and bottom wall portions of said boot.

4. File driving equipment which comprisesla casting shell for a pile, a'driving mandrel having a corecom-- and the upper end of the collar of said boot is tongued to match said corrugations and the tongues arewelded along their edges to said shell.

References Cited in the file of this patent I UNITED STATES PATENTS 869,336 Stewart Oct. 29, 1907 951,668 Welsh Mar. 8, 1910 1,236,556 Goldsborough Aug. 14, 1917 1,700,319 Kjekstad Jan. 29, 1929 1,860,558 Tada May 31,1932 1,910,939 Titcomb May 23, 1933 2,625,015 Cobi Jan. 13, 1953 2,684,577 Smith July 27, 1954- 2,741,093 Riker Apr. 10, 1956 FOREIGN PATENTS 28,652 Great Britain Dec. 15, 1906 361,203 Great Britain Nov. 19,1931 

